Lesson 3: Reaction Quotients

• Reaction Quotient (Q)

  Used to analyze an equilibrium system and can be calculated at any time during the reaction (doesn't have to be at equilibrium)

  
• Calculating Q


  1. aP + bZ ↔ cR + dS

  2. Q = [R]c [S]d / [P]a [Z]b (instantaneous)

  3. Keq = [R]c [S]d / [P]a [Z]b (at equilibrium)
• Comparing Q to K

  • If Q is less than K, it has too many reactants so it is not at equilibrium yet and shifts right
  • If Q = K, it is at equilibrium
  • If Q is greater than K, it has too many products so it has to shift left to be at equilibrium
• Q


  Products / Reactants
• Determining if reaction is at equilibrium

  1. Calculate Q

  2. Compare Q to K

  3. Determine direction of shift if not at equilibrium